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Grant from NASA Supports Study of Pulsars

A highly competitive grant from NASA is supporting a Hope College physicist's research into the presence and nature of the rotating stars known as pulsars.

Dr. Peter Gonthier, a professor of physics, is leading a three-scholar team from two continents in an effort to investigate the potential relationship between positrons - which are a form of electrically charged particle--and gamma ray pulsars. They are using the information to refine computer models, which Gonthier has been developing for NASA for several years, to better understand and locate the stars, which cannot be seen by the naked eye or even detected from earth.

The project is supported by a one-year, $45,161 NASA Fermi Guest Investigator grant that took effect in July.

The research follows what Gonthier described as the major break-through in data-gathering concerning the stars since the 2008 launch of the highly sensitive Fermi Gamma Ray Space Telescope. Where the Fermi telescope's predecessor had discovered seven to eight gamma pulsars during its entire nine-year life, Fermi found about 60 in its first year.

Fermi and other sensitive instruments have also enabled scientists to better locate and track the behavior of the electrically charged positrons that are traveling through space, particles that may offer a clue in the search for the gamma ray pulsars. The pattern that has emerged, Gonthier noted, suggests that some of the positrons are coming from the pulsars.

"There's a lot of excitement over this - what might be happening in our vicinity and where these might be coming from," he said. "It could be that the local source of positrons could be pulsars, particularly millisecond pulsars."

Pulsars are extremely dense neutron stars which have the mass of one and a half of the earth's sun packed within a ball 16 miles in diameter. They rotate rapidly, completing a revolution in a range between once every 10 seconds and a thousand times a second. Highly magnetized, they shoot out a beam of radiation that, given the spinning, makes the star seem to pulse as the beam passes into view.

Pulsars were discovered in the 1960s, when scientists observed radio waves coming from them. The range of electromagnetic radiation, however, is much broader, covering also microwaves, infrared, visible light, ultraviolet light, x-rays and, at the highest end, gamma rays.

Gonthier said that the pulsars that produce radio waves remain the best known - some 1,880 have been recorded - because their emissions are detectable from earth. The gamma radiation, in contrast, requires space-based instruments to discover because earth's atmosphere blocks it. Some pulsars emit gamma radiation but no radio waves, which means that they've been harder to find.

The computer models, Gonthier noted, can help researchers anticipate the presence of additional pulsars by making deductions regarding their presence based on those that are already known and how they behave. The presence of the positrons adds another tool to the mix.

His co-investigators on the project are Dr. Alice Harding, who is on the staff of the Astrophysics Space Division of the NASA Goddard Space Flight Center in Greenbelt, Md., and Dr. Christo Venter, a member of the space physics faculty of the Potchefstroom Campus of North-West University of South Africa. Gonthier has been conducting research with Harding on a variety of NASA-related projects since 1992. All three scientists worked together on the project while at the NASA Goddard Space Flight Center this summer. Gonthier is continuing his work at Hope during the current school year.